1. Field of the Invention
This invention is related to contact lenses and rigid gas permeable (“RGP”) corneal-scleral contact lenses in particular. The lens set forth herein is a progressive vision lens designed to cover the cornea and a small portion of the sclera of the eye.
More particularly, the lens presented here allows for a near center aspheric addition to create a true progressive rigid gas permeable contact lens. The lens will correct for the lack of accommodation “presbyopia” in all eyes that are normal or unaltered and in eyes that have been altered by refractive surgery or any surgical procedure that modifies or changes the shape of the cornea such as transplants.
2. Description of the Art
The art in the contact lens field is replete with innovations in contact lens designs for both post refractive, bifocal and multifocal lenses. However, the application of a progressive multifocal corneal sclera lens that also allows a post refractive lens with the addition of a progressive multifocal in a corneal-scleral lens is unique. The aging population is growing worldwide. Today's refractive surgery patients in most cases had the procedure done to rid them of the need to wear spectacle lenses but as they age they develop presbyopia. This condition renders the eye with a decreasing amount of accommodation or the ability to transition from near to distance vision. The aging population is remaining active longer and requires a lens with continuous vision that can match their active lifestyle. The invention has been successfully used to provide corrections of a surgically altered cornea for myopia, hyperopia, and presbyopia. The lens, by its design, providing a progressive near center aspheric near addition with a diameter that covers both the cornea and a portion of the sclera, allows for a fit that corrects presbyopia in both normal and surgically altered corneas.
The lenses presented here work well in treating patients with visual deficiencies resulting from post refractive surgery errors and age related presbyopia in both normal and surgically altered eyes.
Furthermore, this invention relates to methods of the design and application of lenses and the means to obtain measurements from the eye by the use of pre-op and post-op keratometry readings, diagnostic lenses, topography readings and/or a combination of these.
Corneal contact lenses that are supported entirely on the cornea have problems that are solved through the use of a corneal-scleral lens as presented here. In a corneal lens all the functions of the lens take place on the cornea. This includes both near and distance vision, tear exchange curves for comfort, curves to center the lens and curves for edge contour. Each part of a corneal lens has a fitting duty and in some cases such as a translating or bifocal or multifocal. This presents a distinct problem such as vision and acuity loss during the transitional movement of the lens from the near and distance optical component of the lens. This results in a compromise to continuous vision correction. By placing a progressive multifocal segment in the center of the anterior surface of the lens the result is continuous vision throughout the transition from near to distance vision in a controlled rate. The larger diameter of the corneal-scleral lens, usually between 12.5 and 17.0 mm gives the lens its reliable centering. The larger diameter of the lens is also responsible for its high degree of comfort. This is possible as the edges of the lens are always under both the upper and lower eyelid minimizing the foreign body sensation as the eyelid performs its blinking function. It also increases comfort by distributing the weight and pressure of the lens over the cornea and a small portion of the sclera.
This application is related to rigid gas permeable contact lenses of the type set forth in U.S. Pat. No. 5,929,968 to Cotie and Hirshberg titled Scleral-Corneal Contact Lens which is incorporated by reference in its entirety herein. The lens set forth in U.S. Pat. No. 5,929,968 is a single vision lens for orthokeratology applications and is not a progressive multifocal rigid gas permeable lens.
In contact lenses there are designs to provide for bifocal vision. These designs include the most common type of bifocal contact, the translating bifocal. In this system eyelid contact with the lens will facilitate movement of the lens from a near object focus position to a distance power portion of the lens. In this example the near power is on the bottom of the lens. A system is used to keep the lens from rotating on the eye. When the patient looks downward to focus on a near object the lens translates up so the eye is looking through the near or add power at the bottom of the lens. When the person looks up and blinks the upper eyelid “catches” on the top portion of the lens forcing it downward allowing the patient to use the distance power portion of the lens. Because of the contact of the upper lid with the edge of the lens a comfort issue most often referred to as a foreign body sensation is caused. The use of the translating method also gives the unwanted lost of vision as the lens moves from distance to near during the blinking process.
In other methods of providing bifocal vision a mono vision situation is used to accomplish bifocal vision. This type of vision correction for presbyopes uses two single vision contact lenses one having the prescriptive power of the distance prescription in one eye and the other having the prescription for the near power in the other eye. The problem with this method is “simultaneous vision.” This is were the eyes sees both near and distance at the same time. This method requires the patient to have an adaptation period were the brain is trained to see only the image that it requires and to ignore the other. This can in some patient cause a loss of depth perception. Some patients never fully adjust to this type of vision and the time of adaptation for those who can, varies from a short period of several days to a period of many days. Many patients simply discontinue the use of such contacts.
In this technique two single vision lens are used, one in each eye. One lens will have a prescriptive power of the distance prescription in one eye and the prescriptive power for the near power in the lens for the other eye. A refinement of this lens is to have one of the lenses being a bifocal lens however this has not proven to be a well accepted solution to the need for a bifocal contact lens.
Another method of vision correction in contact lens is the concentric bifocal that uses a system of corrective rings that alternate between near and far vision.
This method is also of the “simultaneous vision” mode where the brain is “seeing” both near and distance and the same time. This causes the patient to undergo the same type of adaptation problems as with monovision lens sets. The number of rings that are available to the eye is dependant upon pupil size, which will vary due to ambient lighting conditions. In most cases at least two rings are available.
With current small diameter rigid gas permeable lenses that float on the eye there is not enough stability for acceptable vision.
Each of these methods of providing bifocal vision have not been successfully and widely adopted as there are fit and comfort issues with each of these lens types. Only very motivated patients have been successful in continuing to wear theses types of lenses.